Immunologic adjuvants are added to vaccines to stimulate the immune system's response to the target antigen, but do not in themselves confer immunity. Adjuvants can act in various ways in presenting an antigen to the immune system. Adjuvants can act as a depot for the antigen presenting the antigen over a long period of time, thus maximizing the immune response before the body clears the antigen. Examples of depot type adjuvants are oil emulsions. Adjuvants can also act as an irritant which causes the body to recruit and amplify immune response. A tetanus, diphtheria, and pertussis vaccine, for example, contains minute quantities of toxins produced by each of the target bacteria, but also contains some aluminum hydroxide. Such aluminum salts are common adjuvants in vaccines sold in the United States and have been used in vaccines for over 70 years. The body's immune system develops an antitoxin to the bacteria's toxins, not to the aluminum, but would not respond enough without the help of the aluminum adjuvant.
Although immunological adjuvants have traditionally been viewed as substances that aid the immune response to antigen, adjuvants have also evolved as substances that can aid in stabilizing formulations of antigens, especially for vaccines administered for animal health
Vaccine preparations have been observed to demonstrate less than robust immune response in vivo, creating a need for the development of enhanced vaccine preparations. However, the exact mechanisms working to inhibit and/or reduce less than robust response to vaccines in vivo remain under study.
All vaccines induce inflammation and any inflammation that is sustained for more than a few hours will result in recruitment of myeloid cells (monocytes and neutrophils) to the site of vaccination and to the vaccine draining lymph nodes. Certain subpopulations of these cells are also referred to as vaccine elicited myeloid cells (VDSC). These cells are also referred to as myeloid derived suppressor cells (MDSC). In certain contexts, prior reports indicate that these inflammatory cells (especially monocytes) recruited to vaccine-draining lymph nodes may actually augment immune response, though information presented in the present disclosure suggests otherwise.
Clodronate is a bisphosphonate drug that kills osteoclasts and other macrophages via induction of apoptosis. When clodronate is incorporated within liposomes (LC), uptake by phagocytic cells such as macrophages is greatly enhanced, resulting in selective targeting of macrophages for killing.24, 25, 36 Some studies report that repeated LC administration is capable of depleting both tumor associated macrophages and myeloid suppressor cells.13, 32, 44 
A need remains in the medical arts for improved vaccine preparations with enhanced ability to provoke robust immune response.